Where does “rōs-i̯e/o” come from?

rōs-i̯e/o (Proto-Indo-European) comes from Proto-Indo-European h₁rṓs.

Ancestry of “rōs-i̯e/o”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	h₁rṓs	—

rōs-i̯e/o — Etymology, Origin & Word History | Etymology Explorer